Private podcast on WordPress

functions.php

// put that in functions.php in your theme
add_filter( 'the_content', $content, 'private_podcast', 10, 1 );
function private_podcast( $content ) {
    if( has_category( 'podcast' ) && ! has_access() ) {
       return "This is a private podcast. Please subscribe here";
    }
    return $content;
}
function has_access() {
    global $_GET;
    return in_array( $_GET['token'], ['token1', 'token2']);
}